Patent GB-685260-A (GB)
Title: Improvements in or relating to reproducing servo-mechanisms
IPC: B23Q35/123
Filed: 1950-12-27
Abstract: 685,260. Electric follow-up systems. SOC. D'ELECTRONIQUE ET D'AUTOMATISME. Dec. 27, 1950 [Dec. 24, 1949], No. 31442/50. Class 40 (i) [Also in Group XXXVI] In a servo-system for driving a cutting tool in correspondence with the path of a profile sensing device (feeler), displacement of the feeler results in the generation of two quadrature voltages, representing the amplitude and sense of the feeler displacement resolved along directions normal to and tangential to the profile surface, respectively. The cutting tool, together with the feeler head, is actuated along two fixed rectangular co-ordinate directions by respective servomotors fed from a computer in which (a) two unidirectional voltages Œ S representing the difference between the magnitude of the feeler displacement and a given reference value, are derived from the quadrature voltages (b) further unidirectional voltages Œ U x , Œ U y  representing components of the feeler displacement in the directions of the quadrature voltages corrected for friction between the feeler and profile are also derived from the quadrature voltages, and (c) the voltages Œ S, Œ U x , Œ U y  are combined so as to produce voltages representing the product of the components Œ Ux and Œ U y  and the rotation matrix R = K [<SP>1-S</SP> S  <SP>-S</SP> 1-S ] where K is a constant. These voltages represent the pick-off voltages resolved along the corresponding cutting tool drive directions and are applied to the motor control circuits. As shown, a pendulous feeler 3, movable substantially only in the plane of the paper, is dragged by a carrier head 4 over a profile 1. The carrier head contains a known device supplied with quadrature voltages from a reference oscillator, and from which two quadrature voltages are derived proportional to the components of the displacement M 0 M of the feeler contact M 0  from its neutral (i.e. zero output) position M, along the normal M,N to the profile surface and along the tangent M 0 T thereto. The cutting tool 5 is driven together with the feeler head 4 by separately excited X, Y motors 14, 15, respectively energized from the computer 34 over amplifiers 16, 17 and generators 18, 19. Each generator is supplied over one of two channels corresponding to the two directions of rotation and, in known manner, feedback channels 22-25 lead over feedback mixing resistors 26-29 to the inputs of amplifiers 16, 17. Fig. 2 shows the stabilized oscillator 37 which supplies a voltage E sin #t to an amplifier 39 and to a phase shifter 38 which supplies E cos #t to amplifier 40. The amplifier outputs E sin #t, E cos #t are fed respectively to output transformers 50. 51 and also to transformers 56, 57 provided with known level stabilizing feedback circuits over rectifiers 44, 47, the rectified feed-. back being added to a reference D.C. source 41, amplified at 42, 43 and re-injected ahead of the amplifiers 39, 40. The transformers 56, 57 are connected to known measuring bridges 58, 59 incorporating at 60, 61, the stators of the carrier head 4, the bridge outputs #x, #y being the components of the vector M,M along M 0 T and M 0 N respectively. The bridge outputs #x, #y are added vectorially in a transformer 62 and amplified at 63 to give an output # # at 65, 66 proportional to the feeler displacement. Computer, Fig. 3. The vector voltage # # supplied by the transformer secondary 65 is rectified at 67 and mixed with a reference voltage derived from a battery 68 and corresponding to the maximum permissible value of # # the resultant voltage being amplified in a stage 71 to give the output Œ S on lines 72, 73 respectively. The vector voltage # # supplied also by the secondary 66, passes through a phase shifter 74, adjusted to compensate for friction between the feeler and profile, to a transformer 75, the outputs 78, 79 of which are applied to phase discriminator-rectifier stages 80, 81 also fed with the voltages E sin #t, E cos #t from the transformer secondaries 52-55, the discriminator outputs Œ Ux, Œ Uy being, fed to the lines 84-87 respectively. The lines 72, 73, 84-87 are connected through mixer resistors 92, 94, 96, 98 to produce the voltages (Ux + Uy + S), (Ux + Uy - S), (Ux - Uy + S), (Ux - Uy - S) on the grids of the first valves of pairs 100, 101, 102, 103, the same voltages, but of opposite sign, being produced by similar mixers 93, 95, 97, 99 on the second valves of the respective pairs. These voltages are squared in the respective valves and the output of each pair fed to an adding stage 104 or 105 by way of balancing networks 110, 111, respectively, to compensate for voltage drifts and ageing of the valves. The appropriate combinations of the squared voltages are taken off at 106-109 and combined in the mixers 112-115 with the appropriate voltage Œ Ux or Œ Uy, which as shown in the Specification, is equivalent to multiplying the components Œ Ux, Œ Uy by the matrix R. These outputs are fed with the feedback voltages derived over resistors 26-29 from the generators 18, 19 to the amplifiers 16, 17. The profile may be dispensed with, voltages simulating the feeler pick-off voltages being supplied by a voltage generator.